Bianca Andreescu, of Canada, reacts after defeating Belinda Bencic, of Switzerland, during the semifinals of the U.S. Open tennis championships Thursday, Sept. 5, 2019, in New York. (AP Photo/Charles Krupa)

VIDEO: Canada’s Bianca Andreescu advances to US Open final vs. Serena Williams

There wasn’t a single break-point opportunity in the first set, which lasted nearly as long as Williams’s entire match and went to the tiebreak.

Andreescu hit 25 winners, more than enough to win the set on their own. But she also made 20 unforced errors, almost enough to lose the set on their own.

But the teenager had some momentum going into the tiebreak, and at one point won eight points in a row before losing three straight.

Bencic was serving first in the set, and it always felt as though she was ahead. She played a more consistent set. And she even had a set point but she still lost it.

The second set was a completely different story as Bencic went up 4-1, and 5-2 — both times with two breaks of serve in hand.

The Swiss player changed her tactics. Instead of moving Andreescu around the court as she had done much of the first set, she upped the velocity on her groundstrokes and moved Andreescu around that way.